Field of the Disclosure
The present disclosure relates to an abnormality diagnosis device for an exhaust gas purification apparatus in an internal combustion engine.
Background
There has been known an NOx selective catalytic reduction catalyst (hereinafter, also referred to simply as an “NOx catalyst”) which purifies (removes or reduces) NOx contained in an exhaust gas from an internal combustion engine by using ammonia as a reducing agent. At the upstream side of this NOx catalyst, there is arranged an addition valve or the like which serves to add ammonia or a precursor of ammonia into the exhaust gas. As the precursor of ammonia, there can be mentioned urea, for example. Hereinafter, the precursor of ammonia or ammonia is also collectively referred to as “a reducing agent”.
Here, there has been known a technology in which a determination of whether clogging has occurred in an addition valve is made by using the value of pressure in a reducing agent passage at the time of returning a reducing agent to a tank (for example, refer to patent literature 1). In addition, in the patent literature 1, it is also further described that the determination of whether clogging has occurred in the addition valve is made based on an amount of pressure drop in the reducing agent passage at the time when the reducing agent was supplied.